Abstract:

Article Preview

The microstructure and phase transformation behavior of Ni-Mn-Fe high-temperature shape memory alloys including Ni40+xFe10Mn50-x (x = 0, 10) were investigated. The results show that both two alloys exhibit single fcc γ phase annealed at 900°C for 1 day. When these quenched alloys are again annealed at 500°C for 20 days, they almost exhibit main tetragonal θ martensite. The microstructural evolutions are consistent with the results of phase transformation measurements. It is clearly found that there is an irreversible phase transformation around 480°C ~ 570°C, which is associated with the formation of tetragonal θ martensite from γ phase. Afterwards, the reversible martensitic transformation occurs during heating and cooling with very high transformation temperature.

Abstract: Using Ti-40mass%Ta-0, -4, -8 and -12mass%Sn alloys, the effect of Sn addition on phase
constitution in the solution treated and quenched state and isochronal heat treatment behavior is
studied by electrical resistivity and Vickers hardness measurements and X-ray diffactometry. To
confirm shape memory effect of some of these alloys, shape-recovery test was also performed.
Orthorhombic martensite,  was identified in Ti-40Sn-0 to 8Sn alloy quenched from 1173K, while
phase was identified in STQed Ti-40Ta-12Sn alloy. On isochronal heat treatment, increases of
resistivity at LN and resistivity ratio were observed in only 8Sn alloy, because these increases are
due to reverse-transformation of  to phase. From result of shape recovery test, shape memory
effect was observed in Ti-40Ta-4 and 8Sn alloys

Abstract: The crystallization and optimization of magnetic properties effects in FeXSiB (X=Cu, V,
Co, Zr, Nb) amorphous alloys were studied by applying X-ray diffraction methods, high resolution
transmission electron microscopy (HRTEM), resistometric and magnetic measurements. The
temperatures of the first and the second stage of crystallization, the 1h optimization annealing
temperature and the Curie temperature were determined for different amorphous alloys. Activation
energies of crystallization process were obtained by applying the Kissinger method. The influence
of alloy additions on optimization effect and crystallization processes was carefully examined.

Abstract: In recent years, there has been an increasing interest in magnetic shape memory alloys (MSMAs) due to their unique ability to produce very large output strains and rapid response frequency. NiMnCoIn is a new-type MSMAs in which a reversible magnetic-field-induced phase transformation is observed. The microstructural evolution in the process of dynamic recrystallization in polycrystalline Ni45Co5Mn36.7In13.3 was studied in the present paper. The experimental results showed that the high deformation temperature and slow strain rate were necessary to achieve perfect dynamic-recrystallizing microstructure in Ni45Co5Mn36.7In13.3 alloy. Precipitates with two sizes were observed. The content of Co in precipitates was higher than that in the matrix alloy, while the content of In was lower than that in the matrix alloy.

Abstract: We have investigated athermal and isothermal martensitic transformations (typical displacive transformations) in Fe–Ni, Fe–Ni–Cr, and Ni-Co-Mn-In alloys under magnetic fields and hydrostatic pressures in order to understand the time-dependent nature of martensitic transformation, that is, the kinetics of martensitic transformation. We have confirmed that the two transformation processes are closely related to each other, that is, the athermal process changes to the isothermal process and the isothermal process changes to the athermal one under a hydrostatic pressure or a magnetic field. These findings can be explained by the phenomenological theory, which gives a unified explanation for the two transformation processes previously proposed by our group.